近四十年来长江源区河流水沙量的变化

长江源区是指直门达水文站以上长江干支流的广大集水区域，是长江的重要水源涵养区。通过统计分析直门达站1957－1999年的43a间年径流量和年输沙量的变化情况，得出几个基本结论：长江源区年径流的变化主要受气候等自然因素的影响，年径流周期性变化较为明显，径流丰水年，偏丰水年出现最多的年份是20世纪60年代和80年代，枯水年和偏枯年出现最多的年份是70和90年代，总体上看40年间节径流基本稳定，但90年代比80年代有趋向偏枯的现象；年输沙量与年径流量的变化基本同步，年输沙量的变化主要取决于年径流量的变化，年输沙量也呈弱周期性变化状态，并有趋向减少的势头，近10a直门达站年径流量呈递减的趋势导致了年输沙量呈相应的变化；长江源区径流量和输沙量年内主要集中在5－10月，分别占年径流量和年输沙量的87．3％和99％；沱沱河由于径流以冰川补给为主，径流量与输沙量的变化呈现出不同的特征。

CHANGES OF RUNOFF AND SEDIMENT IN THE SOURCE REGION OF YANGTZE RIVER DURING THE LAST FOUR DECADES

The source region of Yangtze River includes the catchment area beyond Zimenda hydro-station. It is one of the major water conserving areas for Yangtze River. Through analyzing the data of runoff and sediment across Zimenda hydro-station from 1957 to 1999,we can make the following conclusions: the annual runoff change is mainly dominated by the natural factors such as the climate change, its periodic change being very obvious.The low and partial low flow years appeared frequently in 70s and 90s,while the high and partial high flow appeared frequently in 60s and 80s.However,the annual runoff kept stable in general.When compared with the runoff in 80s,the runoff of 90s tended to be lower; the annual sediment change mainly depended on the annual runoff change.They happened synchronously and were related with each other.The decrease of the annual runoff during the recent decade resulted in the decrease of the annual sediment.The annual runoff and river sediment were concentrated on the months of from May to October, and the runoff and sediment of this period accounted for 87.3% and 99% of the annual total,respectively. Tuotuohe River is one of the three sources of Yangtze River,with its runoff being supplied with the thawed water of the glaciers and the annual runoff and sediment changes have their own characteristics.